1. Field of the Invention
The present invention relates to an instrument for measuring dimensions of a seam portion between the body and the cap of a can which is used as a canning container of foodstuffs, etc.
2. Background Art
A can which is used as a canning container of foodstuffs, etc. is seamed after filling the can with the contents and seaming the cap to the body. A dimensional control of this seam operation is an important measure for judging the can seamability. A process control is necessary to ensure that cans difficult to seam do not occur by regularly inspecting the seam portion of the cans after completion of the seaming process.
FIG. 4(a) is a view showing a seamed can body and cap. FIG. 4(b) is a view showing the section of a seam portion formed by seaming. This seam portion is formed by overlapping a body hook BH formed with edge 1b of the neck portion of the can body rolled in and a cover hook CH formed with edge portion 2a of the can cap rolled in and pressing the overlap strongly. Usually, the seam portion slants outwardly at a microangle of .theta. from an extension line of the can body according to the dismantling of a seaming tool, quality of the can, inner pressure of the can, etc.
An inspection is made from many aspects in order to judge the quality of the seam portion. Usually, respective dimensions are measured for the seaming thickness T, seaming width W, counter sink C, body hook BH, cover hook CH, overlap OL (as shown in FIG. 4(b) and can height H (as shown in FIG. 4(a) the seaming thickness T and seaming width W exceed any defined value among these measured values, poor seaming is likely to occur. Thus, the seaming thickness T and seaming width W are the most important areas to be measured.
The present invention is directed to an instrument for measuring exactly these seaming thickness T and seaming width W.
Conventional methods for measuring seaming thickness T and seaming width W involve a method in which one measures a can using a micrometer for and then enters the measured value on a recording paper. However, this method has inherent problems in the skill required to measure the seaming thickness T and seaming width W by maintaining an accurate measuring angle since the seamed portion is circular and slant; an indicator scale of the micrometer is small and difficult to read; and much time is required to record the measured values.
Equipment has been developed for automatically measuring seamed portions using a device for measuring can seam dimensions as disclosed in Japanese Laid-Open Patent Publn. No. 63-108935. A method for inspecting cans is disclosed in Japanese Laid-Open Patent Publn. No. 64-2744. While these devices are useful for labor-saving, they have the following disadvantages because of their complex structure. For example, much time is spent in exchanging a mold in accordance with the kind of can being measured in confirming the measuring accuracy after exchange of a mold. Further, the device used is large and requires a wide area for installation.